5. Osmoregulation

Question 1

where does osmoregulation takes place

Answer 1

loop of henle

Question 2

what is the role of the loop of henle?

Answer 2

create a low water potential in the medulla of the kidney

Question 3

outline the structure of the loop of henle

Answer 3

• descending limb (permeable to water)
• ascending limb (impermeable to water)
• surrounded by a network of capillaries

Question 4

outline selective reabsorption

Answer 4

• fluid moves into the ascending limb, ions are actively transported out of the filtrate into the tissue fluid
• loss of ions causes filtrate to become less concentrated and have a higher water potential
• sodium ions lower water potential surrounding the medulla, making water potential at the base of the loop more negative
• descending limb is permeable to water, it moves out of the filtrate by osmosis into blood capillary, down its water potential concentration gradient
• this increases the concentration of filtrate, lowering the water potential once again

Question 5

what is the feature of the ascending limb?

Answer 5

it is impermeable to water

Question 6

where does filtrate go after reaching the ascending limb?

Answer 6

the distal convoluted tubule and collecting duct

Question 7

what water potential does the collecting duct have?

Answer 7

high water potential

Question 8

what is the permeability of the membrane in the DCT and collecting duct controlled by?

Answer 8

the hormone called ADH

Question 9

what are changes of the blood detected by?

Answer 9

osmoreceptors in the hypothalamus

Question 10

what happens if the hypothalamus detects that blood water potential is too low

Answer 10

stimulates the posterior pituitary gland to secrete more ADH

Question 11

outline the response when there is a low water potential in the blood

Answer 11

• low concentration detected by osmoreceptors in the hypothalamus
• pituitary gland is stimulated, releasing more ADH
• ADH causes collecting ducts to become more permeable to water
• means more water is reabsorbed back into the blood
• volume of urine decreases, concentration increases

Question 12

outline what happens when there is a high water potential in the blood

Answer 12

• high concentration
• pituitary gland decreases the release of ADH
• ADH causes collecting ducts to become less permeable
• means less water is reabsorbed back into the blood
• volume of blood increases, concentration decreases

Question 13

describe how ADH works

Answer 13

• collecting ducts have cells
  with receptors for ADH on membrane
• contain vesicles with aquaporins (water protein channels)
• ADH binds to these receptors
• causes a chain of enzyme controlled reactions inside the secondary messenger model
• causes vesicles containing aquaporins to move and fuse with the membrane
• making the collecting duct more permeable

Question 14

more ADH in the ____ means more _______ meaning an increase in _______ increasing _____

Answer 14

blood
aquaporins
permeability
reabsorption